An important step in the manufacture of photovoltaic (PV) solar modules is their final test under simulated solar illumination. The manufacture of modules to produce megawatts of solar-generated power requires accurate and rapid testing of tens of thousands of modules. Solar simulators to perform this testing are commercially available from many solar equipment manufacturers. In spite of advances in the performance of these simulators, numerous areas for improvement remain. Specifically, three main issues need to be addressed.
The first issue is spectral accuracy. Solar spectrum standards have been set by two principal organizations, IEC and ASTM International. A Class A simulator spectrum is essentially defined as one that falls within ±25% of the Air Mass 1.5 Global (AM1.5G) spectrum in each of six defined spectral intervals. While such a wide tolerance about a standard spectrum may be acceptable for crystalline silicon modules, it is not adequate for more advanced technologies including many single-junction thin-film approaches (CdTe, CIGS, etc.) and certainly not acceptable for multi junction tandem structures. Specifications beyond Class A have been proposed by Spire Corporation of Bedford, Mass. to meet these more demanding requirements.
The second issue is equipment cost-of-ownership, maintenance, and downtime. Virtually all solar simulators commercially available today utilize xenon flashlamps for their principal source of illumination. Typical lifetimes for these lamps range from a few thousand flashes to as many as 100,000 flashes. Replacement costs are typically in the thousands of dollars per lamp, and while lamp replacement on some units can be made by the user, some simulators require trained factory personnel for lamp replacement. Even at the high end of lamp life, production operation in a 24/7 setting can still require lamp replacement every few months. Solar panel measurement time also contributes to cost-of-ownership in that the proposed LED-based solar simulator can be operated at higher pulse rates than the current xenon lamp units, possibly by a factor of three or more.
The third issue is that easier adjustability of spectral and spatial (irradiance) uniformity is needed. Most currently available simulators utilize optical filters to properly modify the xenon lamp spectrum to achieve one closely resembling AM1.5G. The consequence is that adjustment of the spectrum, if necessary, can only be made by replacing one filter set with a different one. Some simulator manufacturers utilize the approach of dual lamps, one xenon and the other halogen (or a similar incandescent source) to adjust the ratio of short wavelength (<700 nm) light to near infrared (>800 nm) light. While modest adjustments in spectra are not needed for many module types, developers or manufacturers of advanced multi-junction, tandem modules need simulators with simple adjustment.
In summary, solar simulators are needed for measuring the performance of solar cells and solar panels. These instruments currently use filtered high-intensity xenon lamps with poor spectral control, high voltage transients that can adversely affect electronic control circuits, lamp aging and a lack of easily-implemented size scaling. What is needed is a more reliable, low-voltage solid-state, spectrum-adjustable and size-scalable simulator light source approach.